Shell reddish-brown: radii broad, with their upper margins not oblique, or only moderately oblique; sutural edges with plainly denticulated septa: basis porose. Scutum without an adductor ridge; tergum with the spur rather narrow.
Var. (a) (Pl. [8], fig. [10 b], [10 c]), with the shell elongated in its rostro-carinal axis; basis narrow, clasping the stem of a zoophyte; lateral compartments much broader than the almost linear rostrum, carina, and carino-lateral compartments.
Var. (b), with rough longitudinally folded walls, and with the summits of the radii forming an angle of about 45° with the basis.
Fossil in Coralline Crag, Sutton and Gedgrave; attached to foliaceous Bryozoa; Mus. S. Wood, Bowerbank. Var. a, Coralline Crag, Sutton, attached to cylindrical branches of corals; Mus. S. Wood. Var. b, attached to shells, Osnabruck, Hanover, Mus. Lyell; Bünde, Westphalia, Mus. Krantz.
My materials consist of a beautiful series of specimens in Messrs. Wood and Bowerbank’s collections; but unfortunately only a single young specimen had its opercular valves preserved. Not one specimen of the very curious variety (a) had opercular valves, yet I cannot feel any doubt about its being only a variety, caused by its attachment to a thin cylindrical branch of a coral, instead of to a foliaceous Bryozoon; it will, however, be convenient to give a separate description of this very remarkable form. With respect to var. (b), both sets of specimens came to me with the name B. stellaris, of Bronn; but as Bronn distinctly states, that in his species the parietes are porose, and as such is not here the case, this cannot possibly be that species: these specimens did not possess their opercular valves, and therefore cannot be identified with certainty.
General Appearance.—Shell conical, with the orifice rather large, and rhomboidal. The surface is very smooth, except in var. (b.) from the Continent, in which it is rugged and longitudinally folded. The colour is ochreous-brown (chiefly no doubt derived from the imbedding substance) tinged with red. The radii often have a much darker and more distinct red tint; they are sometimes longitudinally striped with dirty white. The radii are broad, with their summits straight, and very slightly oblique; in var. b, however, they slope at an angle of about 45°. Basal diameter of largest specimens .6 of an inch; but this is an unusual size.
Scuta (from a young individual), with the growth ridges little prominent. Internally the articular ridge is moderately prominent, with its lower end very obliquely rounded off; there is no adductor ridge; there is a minute pit for the lateral depressor muscle. Terga, with a slight longitudinal depression extending down to the spur: spur short, with its lower end almost square or truncated, about one fourth of width of valve, and placed at about half its own width from the basi-scutal angle. Internally, the articular ridge is prominent; the crests for the tergal depressores are feebly developed.
Parietes, moderately thick and generally strongly ribbed internally, without parietal pores. Radii, wide, with their upper margins straight, not smooth or rounded, and very slightly (or, in var. b moderately) oblique; their sutural edges have well-developed septa, which are denticulated: the interspaces between the septa are filled up solidly. The alæ have their upper margins oblique: they are only slightly, and sometimes not at all, added to above the level of the opercular membrane: their sutural edges are smooth. The basis is thin, but plainly porose.
Var. (a).—With respect to this remarkable variety, any one would at first think it specifically distinct. The shell is much compressed, or elongated in the rostro-carinal axis, sometimes to a great degree; I have seen a specimen .25 of an inch in this axis and only .1 in its broadest part; but this is a very unusual degree of elongation. The most remarkable character is the extraordinary narrowness of the carina, the carino-lateral compartments, and of the rostrum, compared with the great breadth, especially along the basal margin (Pl. [8], fig. [10 b], [10 c]), of the lateral compartments. The radii are of unusual breadth. The tips of the rostrum and of the lateral compartments are a little arched in, tending to make the shell somewhat globular. The true basis is extremely narrow (fig. [10 c]): it is deeply grooved, from clasping the thin, cylindrical stem of the coral to which it had adhered; and I have seen specimens in which the opposite edges of the groove had met, a tube having been thus actually formed. From the grooved basis, and from the elongation of the shell in the rostro-carinal axis, this species presents so close a general resemblance to [Balanus calceolus], and its allies, that I have seen it in a collection arranged on the same tablet with a fossil specimen of [B. calceolus]. Notwithstanding the above several strongly-marked characters, by which this variety differs from the ordinary form, there is a resemblance in colour and aspect, which though difficult to be described, made me from the first suspect that the two were specifically identical. In no point of real structure is there any difference, excepting that, perhaps, the pores in the basis are here rather smaller; but this might arise from the little development of the peculiar basis. Having come to this conclusion, I was interested by finding a specimen in Mr. Wood’s collection, which had originally fixed itself (judging from the form of the basis) on a cylindrical stem, but which had subsequently grown on to an adjoining flat surface; consequently, one side of the shell presented all the peculiar characters of the present variety, whereas the other side, at the rostral end, was undistinguishable from the ordinary form. The unequal development of the rostrum on the two sides was very striking, and clearly showed how great an effect could be produced by the nature of the surface of attachment.